Improvements relating to equalizers

Abstract

Methods and apparatus adapting equalizers for compensating for signal distortion of a received digital signal are disclosed. The method comprises deriving equalizer settings for a received signal, determining at least one signal parameter of said received signal; and storing the derived equalizer settings together with an indication of the signal parameter. The signal parameter could, for instance, comprise the data rate of the signal. If the signal parameter changes the equalizer is configured to use any stored settings which are appropriate for the new signal parameter. Thus, rather than start an entirely new equalizer adaptation routine every time the signal parameter changes the equalizer will use any stored settings which are appropriate for the changed parameter.

The invention claimed is: 
     
       1. An adaptive equalizer wherein equalizer settings are adjusted in response to a received signal, the adaptive equalizer comprising:
 a working memory to initially store, for at least some signal parameters associated with the received signal, default values for equalizer settings; 
 a buffer coupled to said working memory; and 
 control logic responsive to the received signal and coupled to said working memory and said buffer to:
 determine at least one signal parameter of said received signal; 
 derive equalizer settings for the at least one signal parameter of said received signal using stored default values as initial equalizer settings; 
 record the derived equalizer settings for the at least one signal parameter at a first time in the buffer; 
 determine at a second time whether the at least one signal parameter has changed, and if said at least one signal parameter has not changed, store the contents of the buffer along with the at least one signal parameter in said working memory, and if said at least one signal parameter has changed, discard the contents of the buffer and use any stored settings which are appropriate for the changed signal parameter to adjust the equalizer settings; and 
 reset said stored derived equalizer settings to said default values if no data is received for a predetermined period of time; 
 
 wherein storing derived equalizer settings at said first time in said buffer instead of said working memory reduces an error caused by a change in the signal parameter which has occurred but has not yet been detected. 
 
     
     
       2. An adaptive equalizer as claimed in  claim 1  wherein said at least one signal parameter comprises at least one of: transmission channel, data rate, peak amplitude, pre-emphasis, and edge timing. 
     
     
       3. A method of equalizer adaptation comprising the steps of:
 storing, for at least some signal parameters associated with a received signal, default values for equalizer settings; 
 determining at least one signal parameter of said received signal; 
 deriving equalizer settings for the at least one signal parameter of said received signal using stored default values as initial equalizer settings; 
 storing said derived equalizer settings together with an indication of said at least one signal parameter and, when said at least one signal parameter changes, adjusting the equalizer settings based on any stored settings which are appropriate for the changed signal parameter, wherein storing said derived equalizer settings includes periodically determining whether said at least one signal parameter has changed and, if not, storing the derived equalizer settings; and 
 resetting said stored derived equalizer settings to said default values if no data is received for a predetermined period of time; 
 wherein the step of storing said derived equalizer settings comprises periodically recording the derived equalizer settings at a first time in a buffer separate from a working memory, determining at a second time whether said at least one signal parameter has changed, and if said at least one signal parameter has not changed, storing the contents of the buffer along with the at least one signal parameter in said working memory, and if said at least one signal parameter has changed, discarding the contents of the buffer; 
 wherein storing derived equalizer settings at the first time in said buffer instead of said working memory reduces an error caused by a change in the signal parameter which has occurred but has not yet been detected. 
 
     
     
       4. A method as claimed in  claim 3  wherein said at least one signal parameter comprises at least one of: transmission channel, data rate, peak amplitude, pre-emphasis, and edge timing. 
     
     
       5. An adaptive equalizer system comprising:
 an adaptive equalizer having a signal input and an equalized signal output and provided with control logic, wherein a received signal at said signal input is characterized by at least one signal parameter; 
 read/write memory coupled to said adaptive equalizer, wherein data is stored in and read from said read/write memory by said control logic, said data initially comprising default values for equalizer settings; 
 a buffer separate from said read/write memory and coupled to said adaptive equalizer and to said read/write memory, wherein contents are stored in said buffer by said control logic in response to derived equalizer settings for at least one parameter of the received signal; and 
 wherein said control logic is configured to periodically record derived settings of said adaptive equalizer at a first time in said buffer, determine at a second time whether said at least one signal parameter has changed, and if said at least one signal parameter has not changed, store said contents of the buffer along with said at least one signal parameter in said read/write memory, and if said at least one signal parameter has changed, discard said contents of the buffer; 
 a timer coupled to said control logic of said adaptive equalizer, wherein said timer is used to reset said read/write memory to said default values; 
 wherein storing equalizer settings at the first time in said buffer instead of said read/write memory reduces an error caused by a change in the signal parameter which has occurred but has not yet been detected. 
 
     
     
       6. An adaptive equalizer system as recited in  claim 5  wherein said timer is separate from said adaptive equalizer. 
     
     
       7. An adaptive equalizer system as recited in  claim 5  wherein said timer is a part of said adaptive equalizer.